The present invention relates to a method and apparatus for monitoring the cutting of coke in a coke drum of petroleum refining process. In the refining of petroleum, the residual hydrocarbons that remain after lighter hydrocarbons have been removed to produce other products such as gasoline or diesel oils, is converted to coke. The residual hydrocarbons are converted to coke by heating them in the absence of air and allowing them to cool to form coke. Normally, the heating is done externally to a coke drum and the heated mixture discharged into the drum where it cools and solidifies to form coke. The coke drums are normally vertical, cylindrical drums and after they have been filled solid with coke, the heated residual is shifted to a second drum and the coke removed from the first drum.
The coke is removed from the drum by an operation normally referred to as coke cutting. The normal procedure in coke cutting is to first bore or drill a vertical hole through the coke in the drum and then enlarge the opening by reaming. Both the drilling and reaming are accomplished by utilizing a hydraulic jet which discharges in a downward direction. After the central opening has been enlarged to a diameter sufficient to permit all of the lumps of coke subsequently cut from the drum to fall through the bottom discharge, the boring and reaming operation is suspended. The nozzles on the coke cutting head are then charged to nozzles which are directed in a more horizontal direction. The head is then moved to the top of the drum and periodic slices of the coke are cut. It is normally preferable to cut the coke utilizing nozzles which are directed in a slight upward direction since this produces an inclined surface on the coke shelf that permits the water to drain from the coke and allows the large lumps of coke to fall downward through the bottom of the drum. At the bottom of the drum the coke is crushed to the desired fineness and conveyed to a location where it can be dried prior to further use.
During the coke cutting operation it is desirable to maintain the horizontal jets at a fixed position while rotating until the jets have completely cut through the coke and strike the walls of the coke drum. In the past, reliance has been placed on the operator's skill to determine when the jets are striking the wall of the drum. The operators normally relied upon their hearing and experience to determine when the jets were striking the wall of the drum. It is obvious that if the jets do not strike the wall of the drum, all of the coke will not be removed from the drum while if the jets remain in contact with the walls of the drum for any time, the coke cutting operation will be inefficient and require a longer time than is necessary.